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A mouse embryonic stem (ES) cell line containing an inducible transgene for the proneural gene Neurogl has been used to generate glutamatergic neurons at a high efficiency. The present study used in vitro electrophysiology to establish the timeline for acquiring a functional neuronal phenotype in Neurog1-induced cells exhibiting a neuronal morphology. TTX-sensitive action potentials could be evoked from over 80% of the cells after only 4.5 days in vitro (DIV). These cells uniformly showed rapidly adapting responses to current injection, firing one to three action potentials at the onset of the stimulus. In the absence of Neurog1, a limited number of ES cells adopted a neuronal morphology, but these cells displayed slow calcium depolarizations rather than sodium-based spikes. Voltage-gated [Na.sup.+], [K.sup.+], and [Ca.sup.2+] currents were present in nearly all induced cells as early as 4.5 DIV. The voltage-dependent properties of these currents changed little from 4 to 12 DIV with half-activation voltage varying by < 10 mV for any current type throughout the culture period. This study demonstrates that forced expression of proneural genes can induce ES cells to quickly acquire a functional neuronal phenotype with mature electrophysiological properties. Transient overexpression of Neurog1 may be used in neural repair strategies that require the rapid induction of functional neurons from pluripotent stem cells. neuronal differentiation; neurogenesis; electrophysiology; basic helix-loop-helix; voltage-gated; ion channel doi: 10.1152/ajpcell.00207.2010.

A primary cause of deafness is damage of receptor cells in the inner ear. Clinically, it has been demonstrated that effective functionality can be provided by electrical stimulation of the auditory nerve, thus bypassing damaged receptor cells. However, subsequent to sensory cell loss there is a secondary degeneration of the afferent nerve fibers, resulting in reduced effectiveness of such cochlear prostheses. The effects of neurotrophic factors were tested in a guinea pig cochlear prosthesis model. After chemical deafening to mimic the clinical situation, the neurotrophic factors brain-derived neurotrophic factor and an analogue of ciliary neurotrophic factor were infused directly into the cochlea of the inner ear for 26 days by using an osmotic pump system. An electrode introduced into the cochlea was used to elicit auditory responses just as in patients implanted with cochlear prostheses. Intervention with brain-derived neurotrophic factor and the ciliary neurotrophic factor analogue not only increased the survival of auditory spiral ganglion neurons, but significantly enhanced the functional responsiveness of the auditory system as measured by using electrically evoked auditory brainstem responses. This demonstration that neurotrophin intervention enhances threshold sensitivity within the auditory system will have great clinical importance for the treatment of deaf patients with cochlear prostheses. The findings have direct implications for the enhancement of responsiveness in deafferented peripheral nerves.

A morphological study of the inner ear of heterozygous mice shows asymmetric variations of the horizontal canal and a flattening of the crista ampullaris. This is evident from a dominant mutation that developed in transgenic mice due to insertional mutation in heterozygous mice which have a unique facial appearance. Transgene insertion does not affect the role of the closely knitted ataxia locus, and provides a molecular link to genes at the Twirler area of mouse chromosome 18.